OSPF Application-Specific Link Attributes
draft-ietf-ospf-te-link-attr-reuse-16

Document Type Active Internet-Draft (lsr WG)
Last updated 2020-07-01 (latest revision 2020-06-30)
Replaces draft-ppsenak-ospf-te-link-attr-reuse
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Send notices to Acee Lindem <acee@cisco.com>, Yingzhen Qu <yingzhen.qu@futurewei.com>, aretana.ietf@gmail.com
IANA IANA review state Version Changed - Review Needed
RFC Editor RFC Editor state EDIT
LSR Working Group                                         P. Psenak, Ed.
Internet-Draft                                               L. Ginsberg
Intended status: Standards Track                           Cisco Systems
Expires: January 1, 2021                                   W. Henderickx
                                                                   Nokia
                                                             J. Tantsura
                                                                  Apstra
                                                                J. Drake
                                                        Juniper Networks
                                                           June 30, 2020

               OSPF Application-Specific Link Attributes
               draft-ietf-ospf-te-link-attr-reuse-16.txt

Abstract

   Existing traffic engineering related link attribute advertisements
   have been defined and are used in RSVP-TE deployments.  Since the
   original RSVP-TE use case was defined, additional applications (e.g.,
   Segment Routing Policy, Loop Free Alternate) have been defined that
   also make use of the link attribute advertisements.  In cases where
   multiple applications wish to make use of these link attributes the
   current advertisements do not support application specific values for
   a given attribute nor do they support indication of which
   applications are using the advertised value for a given link.  This
   document introduces new link attribute advertisements in OSPFv2 and
   OSPFv3 that address both of these shortcomings.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 1, 2021.

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Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
   3.  Requirements Discussion . . . . . . . . . . . . . . . . . . .   4
   4.  Existing Advertisement of Link Attributes . . . . . . . . . .   5
   5.  Advertisement of Link Attributes  . . . . . . . . . . . . . .   5
     5.1.  OSPFv2 Extended Link Opaque LSA and OSPFv3 E-Router-LSA .   5
   6.  Advertisement of Application-Specific Values  . . . . . . . .   6
   7.  Reused TE link attributes . . . . . . . . . . . . . . . . . .   9
     7.1.  Shared Risk Link Group (SRLG) . . . . . . . . . . . . . .  10
     7.2.  Extended Metrics  . . . . . . . . . . . . . . . . . . . .  10
     7.3.  Administrative Group  . . . . . . . . . . . . . . . . . .  11
     7.4.  Traffic Engineering Metric  . . . . . . . . . . . . . . .  11
   8.  Maximum Link Bandwidth  . . . . . . . . . . . . . . . . . . .  11
   9.  Considerations for Extended TE Metrics  . . . . . . . . . . .  12
   10. Local Interface IPv6 Address Sub-TLV  . . . . . . . . . . . .  12
   11. Remote Interface IPv6 Address Sub-TLV . . . . . . . . . . . .  12
   12. Attribute Advertisements and Enablement . . . . . . . . . . .  13
   13. Deployment Considerations . . . . . . . . . . . . . . . . . .  14
     13.1.  Use of Legacy RSVP-TE LSA Advertisements . . . . . . . .  14
     13.2.  Interoperability, Backwards Compatibility and Migration
            Concerns . . . . . . . . . . . . . . . . . . . . . . . .  15
       13.2.1.  Multiple Applications: Common Attributes with  RSVP-
                TE . . . . . . . . . . . . . . . . . . . . . . . . .  15
       13.2.2.  Multiple Applications: Some Attributes Not Shared
                with RSVP-TE . . . . . . . . . . . . . . . . . . . .  15
       13.2.3.  Interoperability with Legacy Routers . . . . . . . .  15
       13.2.4.  Use of Application-Specific Advertisements for RSVP-
                TE . . . . . . . . . . . . . . . . . . . . . . . . .  16
   14. Security Considerations . . . . . . . . . . . . . . . . . . .  16
   15. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
     15.1.  OSPFv2 . . . . . . . . . . . . . . . . . . . . . . . . .  17

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     15.2.  OSPFv3 . . . . . . . . . . . . . . . . . . . . . . . . .  18
   16. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  19
   17. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  19
   18. References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     18.1.  Normative References . . . . . . . . . . . . . . . . . .  19
     18.2.  Informative References . . . . . . . . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22

1.  Introduction

   Advertisement of link attributes by the OSPFv2 [RFC2328] and OSPFv3
   [RFC5340] protocols in support of traffic engineering (TE) was
   introduced by [RFC3630] and [RFC5329] respectively.  It has been
   extended by [RFC4203], [RFC7308] and [RFC7471].  Use of these
   extensions has been associated with deployments supporting Traffic
   Engineering over Multiprotocol Label Switching (MPLS) in the presence
   of the Resource Reservation Protocol (RSVP) - more succinctly
   referred to as RSVP-TE [RFC3209].

   For the purposes of this document an application is a technology that
   makes use of link attribute advertisements, examples of which are
   listed in Section 6.

   In recent years new applications have been introduced that have use
   cases for many of the link attributes historically used by RSVP-TE.
   Such applications include Segment Routing (SR) Policy
   [I-D.ietf-spring-segment-routing-policy] and Loop Free Alternates
   (LFA) [RFC5286].  This has introduced ambiguity in that if a
   deployment includes a mix of RSVP-TE support and SR Policy support
   (for example) it is not possible to unambiguously indicate which
   advertisements are to be used by RSVP-TE and which advertisements are
   to be used by SR Policy.  If the topologies are fully congruent this
   may not be an issue, but any incongruence leads to ambiguity.

   An example where this ambiguity causes a problem is a network in that
   RSVP-TE is enabled only on a subset of its links.  A link attribute
   is advertised for the purpose of another application (e.g.  SR
   Policy) for a link that is not enabled for RSVP-TE.  As soon as the
   router that is an RSVP-TE head-end sees the link attribute being
   advertised for that link, it assumes RSVP-TE is enabled on that link,
   even though it is not.  If such RSVP-TE head-end router tries to
   setup an RSVP-TE path via that link, it will result in the path setup
   failure.

   An additional issue arises in cases where both applications are
   supported on a link but the link attribute values associated with
   each application differ.  Current advertisements do not support

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   advertising application-specific values for the same attribute on a
   specific link.

   This document defines extensions that address these issues.  Also, as
   evolution of use cases for link attributes can be expected to
   continue in the years to come, this document defines a solution that
   is easily extensible for the introduction of new applications and new
   use cases.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Requirements Discussion

   As stated previously, evolution of use cases for link attributes can
   be expected to continue.  Therefore, any discussion of existing use
   cases is limited to requirements that are known at the time of this
   writing.  However, in order to determine the functionality required
   beyond what already exists in OSPF, it is only necessary to discuss
   use cases that justify the key points identified in the introduction,
   which are:

   1.  Support for indicating which applications are using the link
       attribute advertisements on a link

   2.  Support for advertising application-specific values for the same
       attribute on a link

   [RFC7855] discusses use cases/requirements for Segment Routing (SR).
   Included among these use cases is SR Policy which is defined in
   [I-D.ietf-spring-segment-routing-policy].  If both RSVP-TE and SR
   Policy are deployed in a network, link attribute advertisements can
   be used by one or both of these applications.  As there is no
   requirement for the link attributes advertised on a given link used
   by SR Policy to be identical to the link attributes advertised on
   that same link used by RSVP-TE, there is a clear requirement to
   indicate independently which link attribute advertisements are to be
   used by each application.

   As the number of applications that may wish to utilize link
   attributes may grow in the future, an additional requirement is that
   the extensions defined allow the association of additional

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   applications to link attributes without altering the format of the
   advertisements or introducing new backwards compatibility issues.

   Finally, there may still be many cases where a single attribute value
   can be shared among multiple applications, so the solution must
   minimize advertising duplicate link/attribute pairs whenever
   possible.

4.  Existing Advertisement of Link Attributes

   There are existing advertisements used in support of RSVP-TE.  These
   advertisements are carried in the OSPFv2 TE Opaque LSA [RFC3630] and
   OSPFv3 Intra-Area-TE-LSA [RFC5329].  Additional RSVP-TE link
   attributes have been defined by [RFC4203], [RFC7308] and [RFC7471].

   Extended Link Opaque LSAs as defined in [RFC7684] for OSPFv2 and
   Extended Router-LSAs [RFC8362] for OSPFv3 are used to advertise link
   attributes that are used by applications other than RSVP-TE or GMPLS
   [RFC4203].  These LSAs were defined as a generic containers for
   distribution of the extended link attributes.

5.  Advertisement of Link Attributes

   This section outlines the solution for advertising link attributes
   originally defined for RSVP-TE or GMPLS when they are used for other
   applications.

5.1.  OSPFv2 Extended Link Opaque LSA and OSPFv3 E-Router-LSA

   Advantages of Extended Link Opaque LSAs as defined in [RFC7684] for
   OSPFv2 and Extended Router-LSAs [RFC8362] for OSPFv3 with respect to
   advertisement of link attributes originally defined for RSVP-TE when
   used in packet networks and in GMPLS:

   1.  Advertisement of the link attributes does not make the link part
       of the RSVP-TE topology.  It avoids any conflicts and is fully
       compatible with [RFC3630] and [RFC5329].

   2.  The OSPFv2 TE Opaque LSA and OSPFv3 Intra-Area-TE-LSA remains
       truly opaque to OSPFv2 and OSPFv3 as originally defined in
       [RFC3630] and [RFC5329] respectively.  Their contents are not
       inspected by OSPF, which instead acts as a pure transport.

   3.  There is a clear distinction between link attributes used by
       RSVP-TE and link attributes used by other OSPFv2 or OSPFv3
       applications.

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   4.  All link attributes that are used by other applications are
       advertised in a single LSA, the Extended Link Opaque LSA in
       OSPFv2 or the OSPFv3 E-Router-LSA [RFC8362] in OSPFv3.

   The disadvantage of this approach is that in rare cases, the same
   link attribute is advertised in both the TE Opaque and Extended Link
   Attribute LSAs in OSPFv2 or the Intra-Area-TE-LSA and E-Router-LSA in
   OSPFv3.

   Extended Link Opaque LSA [RFC7684] and E-Router-LSA [RFC8362] are
   used to advertise any link attributes used for non-RSVP-TE
   applications in OSPFv2 or OSPFv3 respectively, including those that
   have been originally defined for RSVP-TE applications (See
   Section 7).

   TE link attributes used for RSVP-TE/GMPLS continue to use OSPFv2 TE
   Opaque LSA [RFC3630] and OSPFv3 Intra-Area-TE-LSA [RFC5329].

   The format of the link attribute TLVs that have been defined for
   RSVP-TE applications will be kept unchanged even when they are used
   for non-RSVP-TE applications.  Unique code points are allocated for
   these link attribute TLVs from the OSPFv2 Extended Link TLV Sub-TLV
   Registry [RFC7684] and from the OSPFv3 Extended-LSA Sub-TLV Registry
   [RFC8362], as specified in Section 15.

6.  Advertisement of Application-Specific Values

   To allow advertisement of the application-specific values of the link
   attribute, a new Application-Specific Link Attributes (ASLA) sub-TLV
   is defined.  The ASLA sub-TLV is a sub-TLV of the OSPFv2 Extended
   Link TLV [RFC7684] and OSPFv3 Router-Link TLV [RFC8362].

   On top of advertising the link attributes for standardized
   applications, link attributes can be advertised for the purpose of
   applications that are not standardized.  We call such an application
   a "User Defined Application" or "UDA".  These applications are not
   subject to standardization and are outside of the scope of this
   specification.

   The ASLA sub-TLV is an optional sub-TLV of OSPFv2 Extended Link TLV
   and OSPFv3 Router-Link TLV.  Multiple ASLA sub-TLVs can be present in
   its parent TLV when different applications want to control different
   link attributes or when different value of the same attribute needs
   to be advertised by multiple applications.  The ASLA sub-TLV MUST be
   used for advertisement of the link attributes listed at the end on
   this section if these are advertised inside OSPFv2 Extended Link TLV
   and OSPFv3 Router-Link TLV.  It has the following format:

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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  SABM Length  |  UDABM Length |            Reserved           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Standard Application Identifier Bit Mask             |
   +-                                                             -+
   |                            ...                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           User Defined Application Identifier Bit Mask        |
   +-                                                             -+
   |                            ...                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Link Attribute sub-sub-TLVs              |
   +-                                                             -+
   |                            ...                                |

   where:

      Type: 10 (OSPFv2), 11 (OSPFv3)

      Length: variable

      SABM Length: Standard Application Identifier Bit Mask Length in
      octets.  The value MUST be 0, 4 or 8.  If the Standard Application
      Bit Mask is not present, the Standard Application Bit Mask Length
      MUST be set to 0.

      UDABM Length: User Defined Application Identifier Bit Mask Length
      in octets.  The value MUST be 0, 4 or 8.  If the User Defined
      Application Bit Mask is not present, the User Defined Application
      Bit Mask Length MUST be set to 0.

      Standard Application Identifier Bit Mask: Optional set of bits,
      where each bit represents a single standard application.  Bits are
      defined in the Link Attribute Application Identifier Registry,
      which has been defined in [I-D.ietf-isis-te-app].  Current
      assignments are repeated here for informational purpose:

                    0 1 2 3 4 5 6 7 ...
                   +-+-+-+-+-+-+-+-+...
                   |R|S|F|          ...
                   +-+-+-+-+-+-+-+-+...

         Bit-0 (R-bit): RSVP-TE

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         Bit-1 (S-bit): Segment Routing Policy

         Bit-2 (F-bit): Loop Free Alternate (LFA).  Includes all LFA
         types

      User Defined Application Identifier Bit Mask: Optional set of
      bits, where each bit represents a single user defined application.

   If the SABM or UDABM length is other than 0, 4, or 8, the ASLA sub-
   TLV MUST be ignored by the receiver.

   Standard Application Identifier Bits are defined/sent starting with
   Bit 0.  Undefined bits that are transmitted MUST be transmitted as 0
   and MUST be ignored on receipt.  Bits that are not transmitted MUST
   be treated as if they are set to 0 on receipt.  Bits that are not
   supported by an implementation MUST be ignored on receipt.

   User Defined Application Identifier Bits have no relationship to
   Standard Application Identifier Bits and are not managed by IANA or
   any other standards body.  It is recommended that bits are used
   starting with Bit 0 so as to minimize the number of octets required
   to advertise all UDAs.  Undefined bits which are transmitted MUST be
   transmitted as 0 and MUST be ignored on receipt.  Bits that are not
   transmitted MUST be treated as if they are set to 0 on receipt.  Bits
   that are not supported by an implementation MUST be ignored on
   receipt.

   If the link attribute advertisement is intended to be only used by a
   specific set of applications, corresponding Bit Masks MUST be present
   and application-specific bit(s) MUST be set for all applications that
   use the link attributes advertised in the ASLA sub-TLV.

   Application Bit Masks apply to all link attributes that support
   application-specific values and are advertised in the ASLA sub-TLV.

   The advantage of not making the Application Bit Masks part of the
   attribute advertisement itself is that the format of any previously
   defined link attributes can be kept and reused when advertising them
   in the ASLA sub-TLV.

   If the same attribute is advertised in more than one ASLA sub-TLVs
   with the application listed in the Application Bit Masks, the
   application SHOULD use the first instance of advertisement and ignore
   any subsequent advertisements of that attribute.

   If link attributes are advertised with zero length Application
   Identifier Bit Masks for both standard applications and user defined
   applications, then any Standard Application and/or any User Defined

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   Application is permitted to use that set of link attributes.  If
   support for a new application is introduced on any node in a network
   in the presence of such advertisements, these advertisements are
   permitted to be used by the new application.  If this is not what is
   intended, then existing advertisements MUST be readvertised with an
   explicit set of applications specified before a new application is
   introduced.

   An application-specific advertisement (Application Identifier Bit
   Mask with a matching Application Identifier Bit set) for an attribute
   MUST always be preferred over the advertisement of the same attribute
   with the zero length Application Identifier Bit Masks for both
   standard applications and user defined applications on the same link.

   This document defines the initial set of link attributes that MUST
   use the ASLA sub-TLV if advertised in the OSPFv2 Extended Link TLV or
   in the OSPFv3 Router-Link TLV.  Documents which define new link
   attributes MUST state whether the new attributes support application-
   specific values and as such are advertised in an ASLA sub-TLV.  The
   standard link attributes that are advertised in ASLA sub-TLVs are:

      - Shared Risk Link Group [RFC4203]

      - Unidirectional Link Delay [RFC7471]

      - Min/Max Unidirectional Link Delay [RFC7471]

      - Unidirectional Delay Variation [RFC7471]

      - Unidirectional Link Loss [RFC7471]

      - Unidirectional Residual Bandwidth [RFC7471]

      - Unidirectional Available Bandwidth [RFC7471]

      - Unidirectional Utilized Bandwidth [RFC7471]

      - Administrative Group [RFC3630]

      - Extended Administrative Group [RFC7308]

      - TE Metric [RFC3630]

7.  Reused TE link attributes

   This section defines the use case and indicates the code points
   (Section 15) from the OSPFv2 Extended Link TLV Sub-TLV Registry and

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   OSPFv3 Extended-LSA Sub-TLV Registry for some of the link attributes
   that have been originally defined for RSVP-TE or GMPLS.

7.1.  Shared Risk Link Group (SRLG)

   The SRLG of a link can be used in OSPF calculated IPFRR (IP Fast
   Reroute) [RFC5714] to compute a backup path that does not share any
   SRLG group with the protected link.

   To advertise the SRLG of the link in the OSPFv2 Extended Link TLV,
   the same format for the sub-TLV defined in section 1.3 of [RFC4203]
   is used and TLV type 11 is used.  Similarly, for OSPFv3 to advertise
   the SRLG in the OSPFv3 Router-Link TLV, TLV type 12 is used.

7.2.  Extended Metrics

   [RFC3630] defines several link bandwidth types.  [RFC7471] defines
   extended link metrics that are based on link bandwidth, delay and
   loss characteristics.  All of these can be used to compute primary
   and backup paths within an OSPF area to satisfy requirements for
   bandwidth, delay (nominal or worst case) or loss.

   To advertise extended link metrics in the OSPFv2 Extended Link TLV,
   the same format for the sub-TLVs defined in [RFC7471] is used with
   the following TLV types:

      12 - Unidirectional Link Delay

      13 - Min/Max Unidirectional Link Delay

      14 - Unidirectional Delay Variation

      15 - Unidirectional Link Loss

      16 - Unidirectional Residual Bandwidth

      17 - Unidirectional Available Bandwidth

      18 - Unidirectional Utilized Bandwidth

   To advertise extended link metrics in the OSPFv3 Extended-LSA Router-
   Link TLV, the same format for the sub-TLVs defined in [RFC7471] is
   used with the following TLV types:

      13 - Unidirectional Link Delay

      14 - Min/Max Unidirectional Link Delay

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      15 - Unidirectional Delay Variation

      16 - Unidirectional Link Loss

      17 - Unidirectional Residual Bandwidth

      18 - Unidirectional Available Bandwidth

      19 - Unidirectional Utilized Bandwidth

7.3.  Administrative Group

   [RFC3630] and [RFC7308] define the Administrative Group and Extended
   Administrative Group sub-TLVs respectively.

   To advertise the Administrative Group and Extended Administrative
   Group in the OSPFv2 Extended Link TLV, the same format for the sub-
   TLVs defined in [RFC3630] and [RFC7308] is used with the following
   TLV types:

      19 - Administrative Group

      20 - Extended Administrative Group

   To advertise Administrative Group and Extended Administrative Group
   in the OSPFv3 Router-Link TLV, the same format for the sub-TLVs
   defined in [RFC3630] and [RFC7308] is used with the following TLV
   types:

      20 - Administrative Group

      21 - Extended Administrative Group

7.4.  Traffic Engineering Metric

   [RFC3630] defines Traffic Engineering Metric.

   To advertise the Traffic Engineering Metric in the OSPFv2 Extended
   Link TLV, the same format for the sub-TLV defined in section 2.5.5 of
   [RFC3630] is used and TLV type 22 is used.  Similarly, for OSPFv3 to
   advertise the Traffic Engineering Metric in the OSPFv3 Router-Link
   TLV, TLV type 22 is used.

8.  Maximum Link Bandwidth

   Maximum link bandwidth is an application independent attribute of the
   link that is defined in [RFC3630].  Because it is an application
   independent attribute, it MUST NOT be advertised in ASLA sub-TLV.

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   Instead, it MAY be advertised as a sub-TLV of the Extended Link
   Opaque LSA Extended Link TLV in OSPFv2 [RFC7684] or sub-TLV of OSPFv3
   E-Router-LSA Router-Link TLV in OSPFv3 [RFC8362].

   To advertise the Maximum link bandwidth in the OSPFv2 Extended Link
   TLV, the same format for sub-TLV defined in [RFC3630] is used with
   TLV type 23.

   To advertise the Maximum link bandwidth in the OSPFv3 Router-Link
   TLV, the same format for sub-TLV defined in [RFC3630] is used with
   TLV type 23.

9.  Considerations for Extended TE Metrics

   [RFC7471] defines a number of dynamic performance metrics associated
   with a link.  It is conceivable that such metrics could be measured
   specific to traffic associated with a specific application.
   Therefore this document includes support for advertising these link
   attributes specific to a given application.  However, in practice it
   may well be more practical to have these metrics reflect the
   performance of all traffic on the link regardless of application.  In
   such cases, advertisements for these attributes can be associated
   with all of the applications utilizing that link.  This can be done
   either by explicitly specifying the applications in the Application
   Identifier Bit Mask or by using a zero length Application Identifier
   Bit Mask.

10.  Local Interface IPv6 Address Sub-TLV

   The Local Interface IPv6 Address Sub-TLV is an application
   independent attribute of the link that is defined in [RFC5329].
   Because it is an application independent attribute, it MUST NOT be
   advertised in the ASLA sub-TLV.  Instead, it MAY be advertised as a
   sub-TLV of the OSPFv3 E-Router-LSA Router-Link TLV [RFC8362].

   To advertise the Local Interface IPv6 Address Sub-TLV in the OSPFv3
   Router-Link TLV, the same format for sub-TLV defined in [RFC5329] is
   used with TLV type 24.

11.  Remote Interface IPv6 Address Sub-TLV

   The Remote Interface IPv6 Address Sub-TLV is an application
   independent attribute of the link that is defined in [RFC5329].
   Because it is an application independent attribute, it MUST NOT be
   advertised in the ASLA sub-TLV.  Instead, it MAY be advertised as a
   sub-TLV of the OSPFv3 E-Router-LSA Router-Link TLV [RFC8362].

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   To advertise the Remote Interface IPv6 Address Sub-TLV in the OSPFv3
   Router-Link TLV, the same format for sub-TLV defined in [RFC5329] is
   used with TLV type 25.

12.  Attribute Advertisements and Enablement

   This document defines extensions to support the advertisement of
   application-specific link attributes.

   There are applications where the application enablement on the link
   is relevant - e.g., RSVP-TE - one needs to make sure that RSVP is
   enabled on the link before sending a RSVP-TE signaling message over
   it.

   There are applications where the enablement of the application on the
   link is irrelevant and has nothing to do with the fact that some link
   attributes are advertised for the purpose of such application.  An
   example of this is LFA.

   Whether the presence of link attribute advertisements for a given
   application indicates that the application is enabled on that link
   depends upon the application.  Similarly, whether the absence of link
   attribute advertisements indicates that the application is not
   enabled depends upon the application.

   In the case of RSVP-TE, the advertisement of application-specific
   link attributes has no implication of RSVP-TE being enabled on that
   link.  The RSVP-TE enablement is solely derived from the information
   carried in the OSPFv2 TE Opaque LSA [RFC3630] and OSPFv3 Intra-Area-
   TE-LSA [RFC5329].

   In the case of SR Policy, advertisement of application-specific link
   attributes does not indicate enablement of SR Policy.  The
   advertisements are only used to support constraints that may be
   applied when specifying an explicit path.  SR Policy is implicitly
   enabled on all links that are part of the Segment Routing enabled
   topology independent of the existence of link attribute
   advertisements

   In the case of LFA, advertisement of application-specific link
   attributes does not indicate enablement of LFA on that link.
   Enablement is controlled by local configuration.

   If, in the future, additional standard applications are defined to
   use this mechanism, the specification defining this use MUST define
   the relationship between application-specific link attribute
   advertisements and enablement for that application.

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   This document allows the advertisement of application-specific link
   attributes with no application identifiers i.e., both the Standard
   Application Identifier Bit Mask and the User Defined Application
   Identifier Bit Mask are not present (See Section 6).  This supports
   the use of the link attribute by any application.  In the presence of
   an application where the advertisement of link attribute
   advertisements is used to infer the enablement of an application on
   that link (e.g., RSVP-TE), the absence of the application identifier
   leaves ambiguous whether that application is enabled on such a link.
   This needs to be considered when making use of the "any application"
   encoding.

13.  Deployment Considerations

13.1.  Use of Legacy RSVP-TE LSA Advertisements

   Bit Identifiers for Standard Applications are defined in Section 6.
   All of the identifiers defined in this document are associated with
   applications that were already deployed in some networks prior to the
   writing of this document.  Therefore, such applications have been
   deployed using the RSVP-TE LSA advertisements.  The Standard
   Applications defined in this document may continue to use RSVP-TE LSA
   advertisements for a given link so long as at least one of the
   following conditions is true:

      The application is RSVP-TE

      The application is SR Policy or LFA and RSVP-TE is not deployed
      anywhere in the network

      The application is SR Policy or LFA, RSVP-TE is deployed in the
      network, and both the set of links on which SR Policy and/or LFA
      advertisements are required and the attribute values used by SR
      Policy and/or LFA on all such links is fully congruent with the
      links and attribute values used by RSVP-TE

   Under the conditions defined above, implementations that support the
   extensions defined in this document have the choice of using RSVP-TE
   LSA advertisements or application-specific advertisements in support
   of SR Policy and/or LFA.  This will require implementations to
   provide controls specifying which type of advertisements are to be
   sent/ processed on receive for these applications.  Further
   discussion of the associated issues can be found in Section 13.2.

   New applications that future documents define to make use of the
   advertisements defined in this document MUST NOT make use of RSVP-TE
   LSA advertisements.  This simplifies deployment of new applications

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   by eliminating the need to support multiple ways to advertise
   attributes for the new applications.

13.2.  Interoperability, Backwards Compatibility and Migration Concerns

   Existing deployments of RSVP-TE, SR Policy, and/or LFA utilize the
   legacy advertisements listed in Section 4.  Routers which do not
   support the extensions defined in this document will only process
   legacy advertisements and are likely to infer that RSVP-TE is enabled
   on the links for which legacy advertisements exist.  It is expected
   that deployments using the legacy advertisements will persist for a
   significant period of time.  Therefore deployments using the
   extensions defined in this document in the presence of routers that
   do not support these extensions need to be able to interoperate with
   the use of legacy advertisements by the legacy routers.  The
   following sub-sections discuss interoperability and backwards
   compatibility concerns for a number of deployment scenarios.

13.2.1.  Multiple Applications: Common Attributes with RSVP-TE

   In cases where multiple applications are utilizing a given link, one
   of the applications is RSVP-TE, and all link attributes for a given
   link are common to the set of applications utilizing that link,
   interoperability is achieved by using legacy advertisements for RSVP-
   TE.  Attributes for applications other than RSVP-TE MUST be
   advertised using application-specific advertisements.  This results
   in duplicate advertisements for those attributes.

13.2.2.  Multiple Applications: Some Attributes Not Shared with RSVP-TE

   In cases where one or more applications other than RSVP-TE are
   utilizing a given link and one or more link attribute values are not
   shared with RSVP-TE, interoperability is achieved by using legacy
   advertisements for RSVP-TE.  Attributes for applications other than
   RSVP-TE MUST be advertised using application-specific advertisements.
   In cases where some link attributes are shared with RSVP-TE, this
   requires duplicate advertisements for those attributes

13.2.3.  Interoperability with Legacy Routers

   For the applications defined in this document, routers that do not
   support the extensions defined in this document will send and receive
   only legacy link attribute advertisements.  So long as there is any
   legacy router in the network that has any of the applications
   enabled, all routers MUST continue to advertise link attributes using
   legacy advertisements.  In addition, the link attribute values
   associated with the set of applications supported by legacy routers
   (RSVP-TE, SR Policy, and/or LFA) are always shared since legacy

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   routers have no way of advertising or processing application-specific
   values.  Once all legacy routers have been upgraded, migration from
   legacy advertisements to application specific advertisements can be
   achieved via the following steps:

   1)Send new application-specific advertisements while continuing to
   advertise using the legacy advertisement (all advertisements are then
   duplicated).  Receiving routers continue to use legacy
   advertisements.

   2)Enable the use of the application-specific advertisements on all
   routers

   3)Keep legacy advertisements if needed for RSVP-TE purposes.

   When the migration is complete, it then becomes possible to advertise
   incongruent values per application on a given link.

   Documents defining new applications that make use of the application-
   specific advertisements defined in this document MUST discuss
   interoperability and backwards compatibility issues that could occur
   in the presence of routers that do not support the new application.

13.2.4.  Use of Application-Specific Advertisements for RSVP-TE

   The extensions defined in this document support RSVP-TE as one of the
   supported applications.  It is however RECOMMENDED to advertise all
   link-attributes for RSVP-TE in the existing OSPFv2 TE Opaque LSA
   [RFC3630] and OSPFv3 Intra-Area-TE-LSA [RFC5329] to maintain backward
   compatibility.  RSVP-TE can eventually utilize the application-
   specific advertisements for newly defined link attributes, that are
   defined as application-specific.

   Link attributes that are not allowed to be advertised in the ASLA
   Sub-TLV, such as Maximum Reservable Link Bandwidth and Unreserved
   Bandwidth MUST use the OSPFv2 TE Opaque LSA [RFC3630] and OSPFv3
   Intra-Area-TE-LSA [RFC5329] and MUST NOT be advertised in ASLA Sub-
   TLV.

14.  Security Considerations

   Existing security extensions as described in [RFC2328], [RFC5340] and
   [RFC8362] apply to extensions defined in this document.  While OSPF
   is under a single administrative domain, there can be deployments
   where potential attackers have access to one or more networks in the
   OSPF routing domain.  In these deployments, stronger authentication
   mechanisms such as those specified in [RFC5709], [RFC7474], [RFC4552]
   or [RFC7166] SHOULD be used.

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   Implementations must assure that malformed TLV and Sub-TLV defined in
   this document are detected and do not provide a vulnerability for
   attackers to crash the OSPF router or routing process.  Reception of
   a malformed TLV or Sub-TLV SHOULD be counted and/or logged for
   further analysis.  Logging of malformed TLVs and Sub-TLVs SHOULD be
   rate-limited to prevent a Denial of Service (DoS) attack (distributed
   or otherwise) from overloading the OSPF control plane.

   This document defines a new way to advertise link attributes.
   Tampering with the information defined in this document may have an
   effect on applications using it, including impacting Traffic
   Engineering that uses various link attributes for its path
   computation.  This is similar in nature to the impacts associated
   with (for example) [RFC3630].  As the advertisements defined in this
   document limit the scope to specific applications, the impact of
   tampering is similarly limited in scope.

15.  IANA Considerations

   This specifications updates two existing registries:

      - OSPFv2 Extended Link TLV Sub-TLVs Registry

      - OSPFv3 Extended-LSA Sub-TLV Registry

   New values are allocated using the IETF Review procedure as described
   in [RFC5226].

15.1.  OSPFv2

   The OSPFv2 Extended Link TLV Sub-TLVs Registry [RFC7684] defines sub-
   TLVs at any level of nesting for OSPFv2 Extended Link TLVs.  IANA has
   assigned the following Sub-TLV types from the OSPFv2 Extended Link
   TLV Sub-TLVs Registry:

      10 - Application-Specific Link Attributes

      11 - Shared Risk Link Group

      12 - Unidirectional Link Delay

      13 - Min/Max Unidirectional Link Delay

      14 - Unidirectional Delay Variation

      15 - Unidirectional Link Loss

      16 - Unidirectional Residual Bandwidth

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      17 - Unidirectional Available Bandwidth

      18 - Unidirectional Utilized Bandwidth

      19 - Administrative Group

      20 - Extended Administrative Group

      22 - TE Metric

      23 - Maximum Link Bandwidth

15.2.  OSPFv3

   The OSPFv3 Extended-LSA Sub-TLV Registry [RFC8362] defines sub-TLVs
   at any level of nesting for OSPFv3 Extended LSAs.  IANA has assigned
   the following Sub-TLV types from the OSPFv3 Extended-LSA Sub-TLV
   Registry:

      11 - Application-Specific Link Attributes

      12 - Shared Risk Link Group

      13 - Unidirectional Link Delay

      14 - Min/Max Unidirectional Link Delay

      15 - Unidirectional Delay Variation

      16 - Unidirectional Link Loss

      17 - Unidirectional Residual Bandwidth

      18 - Unidirectional Available Bandwidth

      19 - Unidirectional Utilized Bandwidth

      20 - Administrative Group

      21 - Extended Administrative Group

      22 - TE Metric

      23 - Maximum Link Bandwidth

      24 - Local Interface IPv6 Address Sub-TLV

      25 - Remote Interface IPv6 Address Sub-TLV

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16.  Contributors

   The following people contributed to the content of this document and
   should be considered as co-authors:

      Acee Lindem
      Cisco Systems
      301 Midenhall Way
      Cary, NC 27513
      USA

      Email: acee@cisco.com

      Ketan Talaulikar
      Cisco Systems, Inc.
      India

      Email: ketant@cisco.com

      Hannes Gredler
      RtBrick Inc.
      Austria

      Email: hannes@rtbrick.com

17.  Acknowledgments

   Thanks to Chris Bowers for his review and comments.

   Thanks to Alvaro Retana for his detailed review and comments.

18.  References

18.1.  Normative References

   [I-D.ietf-isis-te-app]
              Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and
              J. Drake, "IS-IS Application-Specific Link Attributes",
              draft-ietf-isis-te-app-19 (work in progress), June 2020.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

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   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998,
              <https://www.rfc-editor.org/info/rfc2328>.

   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630,
              DOI 10.17487/RFC3630, September 2003,
              <https://www.rfc-editor.org/info/rfc3630>.

   [RFC4203]  Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in
              Support of Generalized Multi-Protocol Label Switching
              (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005,
              <https://www.rfc-editor.org/info/rfc4203>.

   [RFC5329]  Ishiguro, K., Manral, V., Davey, A., and A. Lindem, Ed.,
              "Traffic Engineering Extensions to OSPF Version 3",
              RFC 5329, DOI 10.17487/RFC5329, September 2008,
              <https://www.rfc-editor.org/info/rfc5329>.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
              <https://www.rfc-editor.org/info/rfc5340>.

   [RFC7308]  Osborne, E., "Extended Administrative Groups in MPLS
              Traffic Engineering (MPLS-TE)", RFC 7308,
              DOI 10.17487/RFC7308, July 2014,
              <https://www.rfc-editor.org/info/rfc7308>.

   [RFC7471]  Giacalone, S., Ward, D., Drake, J., Atlas, A., and S.
              Previdi, "OSPF Traffic Engineering (TE) Metric
              Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015,
              <https://www.rfc-editor.org/info/rfc7471>.

   [RFC7684]  Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
              Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
              Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
              2015, <https://www.rfc-editor.org/info/rfc7684>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8362]  Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
              F. Baker, "OSPFv3 Link State Advertisement (LSA)
              Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
              2018, <https://www.rfc-editor.org/info/rfc8362>.

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18.2.  Informative References

   [I-D.ietf-spring-segment-routing-policy]
              Filsfils, C., Sivabalan, S., Voyer, D., Bogdanov, A., and
              P. Mattes, "Segment Routing Policy Architecture", draft-
              ietf-spring-segment-routing-policy-07 (work in progress),
              May 2020.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
              <https://www.rfc-editor.org/info/rfc3209>.

   [RFC4552]  Gupta, M. and N. Melam, "Authentication/Confidentiality
              for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006,
              <https://www.rfc-editor.org/info/rfc4552>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <https://www.rfc-editor.org/info/rfc5226>.

   [RFC5286]  Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for
              IP Fast Reroute: Loop-Free Alternates", RFC 5286,
              DOI 10.17487/RFC5286, September 2008,
              <https://www.rfc-editor.org/info/rfc5286>.

   [RFC5709]  Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M.,
              Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic
              Authentication", RFC 5709, DOI 10.17487/RFC5709, October
              2009, <https://www.rfc-editor.org/info/rfc5709>.

   [RFC5714]  Shand, M. and S. Bryant, "IP Fast Reroute Framework",
              RFC 5714, DOI 10.17487/RFC5714, January 2010,
              <https://www.rfc-editor.org/info/rfc5714>.

   [RFC7166]  Bhatia, M., Manral, V., and A. Lindem, "Supporting
              Authentication Trailer for OSPFv3", RFC 7166,
              DOI 10.17487/RFC7166, March 2014,
              <https://www.rfc-editor.org/info/rfc7166>.

   [RFC7474]  Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed.,
              "Security Extension for OSPFv2 When Using Manual Key
              Management", RFC 7474, DOI 10.17487/RFC7474, April 2015,
              <https://www.rfc-editor.org/info/rfc7474>.

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Authors' Addresses

   Peter Psenak (editor)
   Cisco Systems
   Eurovea Centre, Central 3
   Pribinova Street 10
   Bratislava  81109
   Slovakia

   Email: ppsenak@cisco.com

   Les Ginsberg
   Cisco Systems
   821 Alder Drive
   MILPITAS, CA  95035
   USA

   Email: ginsberg@cisco.com

   Wim Henderickx
   Nokia
   Copernicuslaan 50
   Antwerp, 2018  94089
   Belgium

   Email: wim.henderickx@nokia.com

   Jeff Tantsura
   Apstra
   US

   Email: jefftant.ietf@gmail.com

   John Drake
   Juniper Networks
   1194 N. Mathilda Ave
   Sunnyvale, California  94089
   USA

   Email: jdrake@juniper.net

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